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Alkylaluminium/Borate systems for activation of metallocene catalysts in ethylene polymerization: ligand effects and reaction parameter optimization.

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Title: Alkylaluminium/Borate systems for activation of metallocene catalysts in ethylene polymerization: ligand effects and reaction parameter optimization.
Authors: Choudhary, Narendra Singh1 (AUTHOR), Mallick, Soumita Basu1 (AUTHOR), Ghar, Priyanka1 (AUTHOR), Pradhan, Narayan C.1 (AUTHOR) ncp@che.iitkgp.ac.in
Source: Journal of Polymer Research. Dec2025, Vol. 32 Issue 12, p1-10. 10p.
Subjects: Metallocene catalysts, Polymerization, Polyethylene, Molecular weights, Ligands (Chemistry), Catalysts, Borates, Alkyl compounds
Abstract: Activation of metallocene catalysts using organoborate compounds in conjunction with alkylaluminium has demonstrated the production of polyolefins with tailored properties over modified methylaluminoxane (MMAO). This study examines the impact of reaction parameters on ethylene polymerization utilizing borate-activated metallocene catalysts in order to identify optimal conditions for catalyst activity and polymer characteristics. It further investigates the synergistic influence of catalyst ligand structures and different alkylaluminium compounds on catalyst activity, molecular weight (MW), and molecular weight distribution (MWD), providing insights into their effects on polymerization pathways. This study employed metallocene catalysts such as Bis(cyclopentadienyl)zirconium dichloride (Zr1), rac-Ethylenebis(indenyl)zirconium dichloride (Zr2), Bis(butylcyclopentadienyl)zirconium dichloride (Zr3) and Bis(cyclopentadienyl)hafnium dichloride (Hf1), activated with either MMAO or Organoborate, alongside cocatalysts triethylaluminium (TEA) and triisobutylaluminium (TIBA) for ethylene polymerization. Catalyst activity, particularly for Zr2, was observed to peak at 80 °C. Additionally, an increase in temperature led to a decrease in polymer MW attributed to accelerated chain transfer reactions, resulting in broader MWD. Catalyst activity was highest in the initial stages of the reaction and diminished as the reaction progressed. Increasing catalyst concentrations from 0.02 × 10–3 to 0.08 × 10–3 mol. L−1 negatively impacted both activity and MW. Similarly, increased borate concentration showed minimal effect on activity and MW. Furthermore, elevating the [Al]/[Zr] ratio increased activity but resulted in shorter polymer chains due to faster chain transfer reactions. The combination of borate with different alkylaluminium cocatalysts exhibited a selective advantage in MW, with the order of preference being TIBA > TIBA + TEA > TEA, as bulkier alkylaluminium limits chain transfer due to steric hindrance. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:Activation of metallocene catalysts using organoborate compounds in conjunction with alkylaluminium has demonstrated the production of polyolefins with tailored properties over modified methylaluminoxane (MMAO). This study examines the impact of reaction parameters on ethylene polymerization utilizing borate-activated metallocene catalysts in order to identify optimal conditions for catalyst activity and polymer characteristics. It further investigates the synergistic influence of catalyst ligand structures and different alkylaluminium compounds on catalyst activity, molecular weight (MW), and molecular weight distribution (MWD), providing insights into their effects on polymerization pathways. This study employed metallocene catalysts such as Bis(cyclopentadienyl)zirconium dichloride (Zr1), rac-Ethylenebis(indenyl)zirconium dichloride (Zr2), Bis(butylcyclopentadienyl)zirconium dichloride (Zr3) and Bis(cyclopentadienyl)hafnium dichloride (Hf1), activated with either MMAO or Organoborate, alongside cocatalysts triethylaluminium (TEA) and triisobutylaluminium (TIBA) for ethylene polymerization. Catalyst activity, particularly for Zr2, was observed to peak at 80 °C. Additionally, an increase in temperature led to a decrease in polymer MW attributed to accelerated chain transfer reactions, resulting in broader MWD. Catalyst activity was highest in the initial stages of the reaction and diminished as the reaction progressed. Increasing catalyst concentrations from 0.02 × 10–3 to 0.08 × 10–3 mol. L−1 negatively impacted both activity and MW. Similarly, increased borate concentration showed minimal effect on activity and MW. Furthermore, elevating the [Al]/[Zr] ratio increased activity but resulted in shorter polymer chains due to faster chain transfer reactions. The combination of borate with different alkylaluminium cocatalysts exhibited a selective advantage in MW, with the order of preference being TIBA > TIBA + TEA > TEA, as bulkier alkylaluminium limits chain transfer due to steric hindrance. [ABSTRACT FROM AUTHOR]
ISSN:10229760
DOI:10.1007/s10965-025-04673-w